What mutation is known in the yellow mouse and how is it inherited? - briefly
The yellow coat results from an X‑linked recessive mutation (the Y allele) that alters pigment synthesis, causing excess pheomelanin. Males display the phenotype when they inherit the allele, while females require two copies to be phenotypically yellow.
What mutation is known in the yellow mouse and how is it inherited? - in detail
The yellow coat in laboratory mice results from a dominant mutation at the agouti locus, designated Ay. Molecular analysis shows that the Ay allele carries a large deletion that juxtaposes a strong, ectopic promoter to the agouti transcription unit. This rearrangement drives continuous expression of agouti signaling protein in melanocytes, shifting melanin synthesis from dark eumelanin to light pheomelanin and producing the characteristic yellow fur.
Inheritance follows an autosomal‑dominant pattern. A single copy of Ay (Ay/+) yields the yellow phenotype. Homozygosity (Ay/Ay) is lethal; embryos carrying two copies fail to develop past the perinatal stage. Consequently, breeding schemes must avoid mating two yellow individuals to prevent loss of offspring. The allele can be transmitted by either sex, and penetrance in heterozygotes is complete under standard laboratory conditions.
Key genetic features:
- Locus: Chromosome 2, agouti (A) gene region.
- Mutation type: Deletion‑insertion that creates a novel promoter upstream of agouti.
- Effect on pigment pathway: Persistent agouti protein antagonizes melanocortin‑1 receptor, favoring pheomelanin production.
- Phenotypic expression: Uniform yellow coat, associated obesity and hyperphagia in heterozygotes.
- Transmission: Autosomal dominant; heterozygous carriers are viable, homozygous carriers are non‑viable.
Understanding this mutation provides a model for studying gene regulation, pigment biology, and the consequences of dominant lethal alleles in mammals.